<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html lang="en">
<head>
<title>Source code</title>
<link rel="stylesheet" type="text/css" href="../../../../../stylesheet.css" title="Style">
</head>
<body>
<div class="sourceContainer">
<pre><span class="sourceLineNo">001</span>/*<a name="line.1"></a>
<span class="sourceLineNo">002</span> * Copyright (C) 2011 The Guava Authors<a name="line.2"></a>
<span class="sourceLineNo">003</span> *<a name="line.3"></a>
<span class="sourceLineNo">004</span> * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except<a name="line.4"></a>
<span class="sourceLineNo">005</span> * in compliance with the License. You may obtain a copy of the License at<a name="line.5"></a>
<span class="sourceLineNo">006</span> *<a name="line.6"></a>
<span class="sourceLineNo">007</span> * http://www.apache.org/licenses/LICENSE-2.0<a name="line.7"></a>
<span class="sourceLineNo">008</span> *<a name="line.8"></a>
<span class="sourceLineNo">009</span> * Unless required by applicable law or agreed to in writing, software distributed under the License<a name="line.9"></a>
<span class="sourceLineNo">010</span> * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express<a name="line.10"></a>
<span class="sourceLineNo">011</span> * or implied. See the License for the specific language governing permissions and limitations under<a name="line.11"></a>
<span class="sourceLineNo">012</span> * the License.<a name="line.12"></a>
<span class="sourceLineNo">013</span> */<a name="line.13"></a>
<span class="sourceLineNo">014</span><a name="line.14"></a>
<span class="sourceLineNo">015</span>package com.google.common.hash;<a name="line.15"></a>
<span class="sourceLineNo">016</span><a name="line.16"></a>
<span class="sourceLineNo">017</span>import static com.google.common.base.Preconditions.checkArgument;<a name="line.17"></a>
<span class="sourceLineNo">018</span>import static com.google.common.base.Preconditions.checkNotNull;<a name="line.18"></a>
<span class="sourceLineNo">019</span><a name="line.19"></a>
<span class="sourceLineNo">020</span>import com.google.common.annotations.Beta;<a name="line.20"></a>
<span class="sourceLineNo">021</span>import com.google.common.annotations.VisibleForTesting;<a name="line.21"></a>
<span class="sourceLineNo">022</span>import com.google.common.base.Objects;<a name="line.22"></a>
<span class="sourceLineNo">023</span>import com.google.common.base.Predicate;<a name="line.23"></a>
<span class="sourceLineNo">024</span>import com.google.common.hash.BloomFilterStrategies.BitArray;<a name="line.24"></a>
<span class="sourceLineNo">025</span><a name="line.25"></a>
<span class="sourceLineNo">026</span>import java.io.Serializable;<a name="line.26"></a>
<span class="sourceLineNo">027</span><a name="line.27"></a>
<span class="sourceLineNo">028</span>import javax.annotation.Nullable;<a name="line.28"></a>
<span class="sourceLineNo">029</span><a name="line.29"></a>
<span class="sourceLineNo">030</span>/**<a name="line.30"></a>
<span class="sourceLineNo">031</span> * A Bloom filter for instances of {@code T}. A Bloom filter offers an approximate containment test<a name="line.31"></a>
<span class="sourceLineNo">032</span> * with one-sided error: if it claims that an element is contained in it, this might be in error,<a name="line.32"></a>
<span class="sourceLineNo">033</span> * but if it claims that an element is &lt;i&gt;not&lt;/i&gt; contained in it, then this is definitely true.<a name="line.33"></a>
<span class="sourceLineNo">034</span> *<a name="line.34"></a>
<span class="sourceLineNo">035</span> * &lt;p&gt;If you are unfamiliar with Bloom filters, this nice<a name="line.35"></a>
<span class="sourceLineNo">036</span> * &lt;a href="http://llimllib.github.com/bloomfilter-tutorial/"&gt;tutorial&lt;/a&gt; may help you understand<a name="line.36"></a>
<span class="sourceLineNo">037</span> * how they work.<a name="line.37"></a>
<span class="sourceLineNo">038</span> *<a name="line.38"></a>
<span class="sourceLineNo">039</span> * &lt;p&gt;The false positive probability ({@code FPP}) of a bloom filter is defined as the probability<a name="line.39"></a>
<span class="sourceLineNo">040</span> * that {@linkplain #mightContain(Object)} will erroneously return {@code true} for an object that<a name="line.40"></a>
<span class="sourceLineNo">041</span> * has not actually been put in the {@code BloomFilter}.<a name="line.41"></a>
<span class="sourceLineNo">042</span> *<a name="line.42"></a>
<span class="sourceLineNo">043</span> *<a name="line.43"></a>
<span class="sourceLineNo">044</span> * @param &lt;T&gt; the type of instances that the {@code BloomFilter} accepts<a name="line.44"></a>
<span class="sourceLineNo">045</span> * @author Dimitris Andreou<a name="line.45"></a>
<span class="sourceLineNo">046</span> * @author Kevin Bourrillion<a name="line.46"></a>
<span class="sourceLineNo">047</span> * @since 11.0<a name="line.47"></a>
<span class="sourceLineNo">048</span> */<a name="line.48"></a>
<span class="sourceLineNo">049</span>@Beta<a name="line.49"></a>
<span class="sourceLineNo">050</span>public final class BloomFilter&lt;T&gt; implements Predicate&lt;T&gt;, Serializable {<a name="line.50"></a>
<span class="sourceLineNo">051</span>  /**<a name="line.51"></a>
<span class="sourceLineNo">052</span>   * A strategy to translate T instances, to {@code numHashFunctions} bit indexes.<a name="line.52"></a>
<span class="sourceLineNo">053</span>   *<a name="line.53"></a>
<span class="sourceLineNo">054</span>   * &lt;p&gt;Implementations should be collections of pure functions (i.e. stateless).<a name="line.54"></a>
<span class="sourceLineNo">055</span>   */<a name="line.55"></a>
<span class="sourceLineNo">056</span>  interface Strategy extends java.io.Serializable {<a name="line.56"></a>
<span class="sourceLineNo">057</span><a name="line.57"></a>
<span class="sourceLineNo">058</span>    /**<a name="line.58"></a>
<span class="sourceLineNo">059</span>     * Sets {@code numHashFunctions} bits of the given bit array, by hashing a user element.<a name="line.59"></a>
<span class="sourceLineNo">060</span>     *<a name="line.60"></a>
<span class="sourceLineNo">061</span>     * &lt;p&gt;Returns whether any bits changed as a result of this operation.<a name="line.61"></a>
<span class="sourceLineNo">062</span>     */<a name="line.62"></a>
<span class="sourceLineNo">063</span>    &lt;T&gt; boolean put(T object, Funnel&lt;? super T&gt; funnel, int numHashFunctions, BitArray bits);<a name="line.63"></a>
<span class="sourceLineNo">064</span><a name="line.64"></a>
<span class="sourceLineNo">065</span>    /**<a name="line.65"></a>
<span class="sourceLineNo">066</span>     * Queries {@code numHashFunctions} bits of the given bit array, by hashing a user element;<a name="line.66"></a>
<span class="sourceLineNo">067</span>     * returns {@code true} if and only if all selected bits are set.<a name="line.67"></a>
<span class="sourceLineNo">068</span>     */<a name="line.68"></a>
<span class="sourceLineNo">069</span>    &lt;T&gt; boolean mightContain(<a name="line.69"></a>
<span class="sourceLineNo">070</span>        T object, Funnel&lt;? super T&gt; funnel, int numHashFunctions, BitArray bits);<a name="line.70"></a>
<span class="sourceLineNo">071</span><a name="line.71"></a>
<span class="sourceLineNo">072</span>    /**<a name="line.72"></a>
<span class="sourceLineNo">073</span>     * Identifier used to encode this strategy, when marshalled as part of a BloomFilter.<a name="line.73"></a>
<span class="sourceLineNo">074</span>     * Only values in the [-128, 127] range are valid for the compact serial form.<a name="line.74"></a>
<span class="sourceLineNo">075</span>     * Non-negative values are reserved for enums defined in BloomFilterStrategies;<a name="line.75"></a>
<span class="sourceLineNo">076</span>     * negative values are reserved for any custom, stateful strategy we may define<a name="line.76"></a>
<span class="sourceLineNo">077</span>     * (e.g. any kind of strategy that would depend on user input).<a name="line.77"></a>
<span class="sourceLineNo">078</span>     */<a name="line.78"></a>
<span class="sourceLineNo">079</span>    int ordinal();<a name="line.79"></a>
<span class="sourceLineNo">080</span>  }<a name="line.80"></a>
<span class="sourceLineNo">081</span><a name="line.81"></a>
<span class="sourceLineNo">082</span>  /** The bit set of the BloomFilter (not necessarily power of 2!)*/<a name="line.82"></a>
<span class="sourceLineNo">083</span>  private final BitArray bits;<a name="line.83"></a>
<span class="sourceLineNo">084</span><a name="line.84"></a>
<span class="sourceLineNo">085</span>  /** Number of hashes per element */<a name="line.85"></a>
<span class="sourceLineNo">086</span>  private final int numHashFunctions;<a name="line.86"></a>
<span class="sourceLineNo">087</span><a name="line.87"></a>
<span class="sourceLineNo">088</span>  /** The funnel to translate Ts to bytes */<a name="line.88"></a>
<span class="sourceLineNo">089</span>  private final Funnel&lt;T&gt; funnel;<a name="line.89"></a>
<span class="sourceLineNo">090</span><a name="line.90"></a>
<span class="sourceLineNo">091</span>  /**<a name="line.91"></a>
<span class="sourceLineNo">092</span>   * The strategy we employ to map an element T to {@code numHashFunctions} bit indexes.<a name="line.92"></a>
<span class="sourceLineNo">093</span>   */<a name="line.93"></a>
<span class="sourceLineNo">094</span>  private final Strategy strategy;<a name="line.94"></a>
<span class="sourceLineNo">095</span><a name="line.95"></a>
<span class="sourceLineNo">096</span>  /**<a name="line.96"></a>
<span class="sourceLineNo">097</span>   * Creates a BloomFilter.<a name="line.97"></a>
<span class="sourceLineNo">098</span>   */<a name="line.98"></a>
<span class="sourceLineNo">099</span>  private BloomFilter(BitArray bits, int numHashFunctions, Funnel&lt;T&gt; funnel,<a name="line.99"></a>
<span class="sourceLineNo">100</span>      Strategy strategy) {<a name="line.100"></a>
<span class="sourceLineNo">101</span>    checkArgument(numHashFunctions &gt; 0,<a name="line.101"></a>
<span class="sourceLineNo">102</span>        "numHashFunctions (%s) must be &gt; 0", numHashFunctions);<a name="line.102"></a>
<span class="sourceLineNo">103</span>    checkArgument(numHashFunctions &lt;= 255,<a name="line.103"></a>
<span class="sourceLineNo">104</span>        "numHashFunctions (%s) must be &lt;= 255", numHashFunctions);<a name="line.104"></a>
<span class="sourceLineNo">105</span>    this.bits = checkNotNull(bits);<a name="line.105"></a>
<span class="sourceLineNo">106</span>    this.numHashFunctions = numHashFunctions;<a name="line.106"></a>
<span class="sourceLineNo">107</span>    this.funnel = checkNotNull(funnel);<a name="line.107"></a>
<span class="sourceLineNo">108</span>    this.strategy = checkNotNull(strategy);<a name="line.108"></a>
<span class="sourceLineNo">109</span>  }<a name="line.109"></a>
<span class="sourceLineNo">110</span><a name="line.110"></a>
<span class="sourceLineNo">111</span>  /**<a name="line.111"></a>
<span class="sourceLineNo">112</span>   * Creates a new {@code BloomFilter} that's a copy of this instance. The new instance is equal to<a name="line.112"></a>
<span class="sourceLineNo">113</span>   * this instance but shares no mutable state.<a name="line.113"></a>
<span class="sourceLineNo">114</span>   *<a name="line.114"></a>
<span class="sourceLineNo">115</span>   * @since 12.0<a name="line.115"></a>
<span class="sourceLineNo">116</span>   */<a name="line.116"></a>
<span class="sourceLineNo">117</span>  public BloomFilter&lt;T&gt; copy() {<a name="line.117"></a>
<span class="sourceLineNo">118</span>    return new BloomFilter&lt;T&gt;(bits.copy(), numHashFunctions, funnel, strategy);<a name="line.118"></a>
<span class="sourceLineNo">119</span>  }<a name="line.119"></a>
<span class="sourceLineNo">120</span><a name="line.120"></a>
<span class="sourceLineNo">121</span>  /**<a name="line.121"></a>
<span class="sourceLineNo">122</span>   * Returns {@code true} if the element &lt;i&gt;might&lt;/i&gt; have been put in this Bloom filter,<a name="line.122"></a>
<span class="sourceLineNo">123</span>   * {@code false} if this is &lt;i&gt;definitely&lt;/i&gt; not the case.<a name="line.123"></a>
<span class="sourceLineNo">124</span>   */<a name="line.124"></a>
<span class="sourceLineNo">125</span>  public boolean mightContain(T object) {<a name="line.125"></a>
<span class="sourceLineNo">126</span>    return strategy.mightContain(object, funnel, numHashFunctions, bits);<a name="line.126"></a>
<span class="sourceLineNo">127</span>  }<a name="line.127"></a>
<span class="sourceLineNo">128</span><a name="line.128"></a>
<span class="sourceLineNo">129</span>  /**<a name="line.129"></a>
<span class="sourceLineNo">130</span>   * Equivalent to {@link #mightContain}; provided only to satisfy the {@link Predicate} interface.<a name="line.130"></a>
<span class="sourceLineNo">131</span>   * When using a reference of type {@code BloomFilter}, always invoke {@link #mightContain}<a name="line.131"></a>
<span class="sourceLineNo">132</span>   * directly instead.<a name="line.132"></a>
<span class="sourceLineNo">133</span>   */<a name="line.133"></a>
<span class="sourceLineNo">134</span>  @Override public boolean apply(T input) {<a name="line.134"></a>
<span class="sourceLineNo">135</span>    return mightContain(input);<a name="line.135"></a>
<span class="sourceLineNo">136</span>  }<a name="line.136"></a>
<span class="sourceLineNo">137</span><a name="line.137"></a>
<span class="sourceLineNo">138</span>  /**<a name="line.138"></a>
<span class="sourceLineNo">139</span>   * Puts an element into this {@code BloomFilter}. Ensures that subsequent invocations of<a name="line.139"></a>
<span class="sourceLineNo">140</span>   * {@link #mightContain(Object)} with the same element will always return {@code true}.<a name="line.140"></a>
<span class="sourceLineNo">141</span>   *<a name="line.141"></a>
<span class="sourceLineNo">142</span>   * @return true if the bloom filter's bits changed as a result of this operation. If the bits<a name="line.142"></a>
<span class="sourceLineNo">143</span>   *     changed, this is &lt;i&gt;definitely&lt;/i&gt; the first time {@code object} has been added to the<a name="line.143"></a>
<span class="sourceLineNo">144</span>   *     filter. If the bits haven't changed, this &lt;i&gt;might&lt;/i&gt; be the first time {@code object}<a name="line.144"></a>
<span class="sourceLineNo">145</span>   *     has been added to the filter. Note that {@code put(t)} always returns the<a name="line.145"></a>
<span class="sourceLineNo">146</span>   *     &lt;i&gt;opposite&lt;/i&gt; result to what {@code mightContain(t)} would have returned at the time<a name="line.146"></a>
<span class="sourceLineNo">147</span>   *     it is called."<a name="line.147"></a>
<span class="sourceLineNo">148</span>   * @since 12.0 (present in 11.0 with {@code void} return type})<a name="line.148"></a>
<span class="sourceLineNo">149</span>   */<a name="line.149"></a>
<span class="sourceLineNo">150</span>  public boolean put(T object) {<a name="line.150"></a>
<span class="sourceLineNo">151</span>    return strategy.put(object, funnel, numHashFunctions, bits);<a name="line.151"></a>
<span class="sourceLineNo">152</span>  }<a name="line.152"></a>
<span class="sourceLineNo">153</span><a name="line.153"></a>
<span class="sourceLineNo">154</span>  /**<a name="line.154"></a>
<span class="sourceLineNo">155</span>   * Returns the probability that {@linkplain #mightContain(Object)} will erroneously return<a name="line.155"></a>
<span class="sourceLineNo">156</span>   * {@code true} for an object that has not actually been put in the {@code BloomFilter}.<a name="line.156"></a>
<span class="sourceLineNo">157</span>   *<a name="line.157"></a>
<span class="sourceLineNo">158</span>   * &lt;p&gt;Ideally, this number should be close to the {@code fpp} parameter<a name="line.158"></a>
<span class="sourceLineNo">159</span>   * passed in {@linkplain #create(Funnel, int, double)}, or smaller. If it is<a name="line.159"></a>
<span class="sourceLineNo">160</span>   * significantly higher, it is usually the case that too many elements (more than<a name="line.160"></a>
<span class="sourceLineNo">161</span>   * expected) have been put in the {@code BloomFilter}, degenerating it.<a name="line.161"></a>
<span class="sourceLineNo">162</span>   *<a name="line.162"></a>
<span class="sourceLineNo">163</span>   * @since 14.0 (since 11.0 as expectedFalsePositiveProbability())<a name="line.163"></a>
<span class="sourceLineNo">164</span>   */<a name="line.164"></a>
<span class="sourceLineNo">165</span>  public double expectedFpp() {<a name="line.165"></a>
<span class="sourceLineNo">166</span>    // You down with FPP? (Yeah you know me!) Who's down with FPP? (Every last homie!)<a name="line.166"></a>
<span class="sourceLineNo">167</span>    return Math.pow((double) bits.bitCount() / bits.size(), numHashFunctions);<a name="line.167"></a>
<span class="sourceLineNo">168</span>  }<a name="line.168"></a>
<span class="sourceLineNo">169</span><a name="line.169"></a>
<span class="sourceLineNo">170</span>  /**<a name="line.170"></a>
<span class="sourceLineNo">171</span>   * @deprecated Use {@link #expectedFpp} instead.<a name="line.171"></a>
<span class="sourceLineNo">172</span>   */<a name="line.172"></a>
<span class="sourceLineNo">173</span>  @Deprecated<a name="line.173"></a>
<span class="sourceLineNo">174</span>  public double expectedFalsePositiveProbability() {<a name="line.174"></a>
<span class="sourceLineNo">175</span>    return expectedFpp();<a name="line.175"></a>
<span class="sourceLineNo">176</span>  }<a name="line.176"></a>
<span class="sourceLineNo">177</span><a name="line.177"></a>
<span class="sourceLineNo">178</span>  @Override<a name="line.178"></a>
<span class="sourceLineNo">179</span>  public boolean equals(@Nullable Object object) {<a name="line.179"></a>
<span class="sourceLineNo">180</span>    if (object == this) {<a name="line.180"></a>
<span class="sourceLineNo">181</span>      return true;<a name="line.181"></a>
<span class="sourceLineNo">182</span>    }<a name="line.182"></a>
<span class="sourceLineNo">183</span>    if (object instanceof BloomFilter) {<a name="line.183"></a>
<span class="sourceLineNo">184</span>      BloomFilter&lt;?&gt; that = (BloomFilter&lt;?&gt;) object;<a name="line.184"></a>
<span class="sourceLineNo">185</span>      return this.numHashFunctions == that.numHashFunctions<a name="line.185"></a>
<span class="sourceLineNo">186</span>          &amp;&amp; this.funnel.equals(that.funnel)<a name="line.186"></a>
<span class="sourceLineNo">187</span>          &amp;&amp; this.bits.equals(that.bits)<a name="line.187"></a>
<span class="sourceLineNo">188</span>          &amp;&amp; this.strategy.equals(that.strategy);<a name="line.188"></a>
<span class="sourceLineNo">189</span>    }<a name="line.189"></a>
<span class="sourceLineNo">190</span>    return false;<a name="line.190"></a>
<span class="sourceLineNo">191</span>  }<a name="line.191"></a>
<span class="sourceLineNo">192</span><a name="line.192"></a>
<span class="sourceLineNo">193</span>  @Override<a name="line.193"></a>
<span class="sourceLineNo">194</span>  public int hashCode() {<a name="line.194"></a>
<span class="sourceLineNo">195</span>    return Objects.hashCode(numHashFunctions, funnel, strategy, bits);<a name="line.195"></a>
<span class="sourceLineNo">196</span>  }<a name="line.196"></a>
<span class="sourceLineNo">197</span><a name="line.197"></a>
<span class="sourceLineNo">198</span>  /**<a name="line.198"></a>
<span class="sourceLineNo">199</span>   * Creates a {@code Builder} of a {@link BloomFilter BloomFilter&lt;T&gt;}, with the expected number<a name="line.199"></a>
<span class="sourceLineNo">200</span>   * of insertions and expected false positive probability.<a name="line.200"></a>
<span class="sourceLineNo">201</span>   *<a name="line.201"></a>
<span class="sourceLineNo">202</span>   * &lt;p&gt;Note that overflowing a {@code BloomFilter} with significantly more elements<a name="line.202"></a>
<span class="sourceLineNo">203</span>   * than specified, will result in its saturation, and a sharp deterioration of its<a name="line.203"></a>
<span class="sourceLineNo">204</span>   * false positive probability.<a name="line.204"></a>
<span class="sourceLineNo">205</span>   *<a name="line.205"></a>
<span class="sourceLineNo">206</span>   * &lt;p&gt;The constructed {@code BloomFilter&lt;T&gt;} will be serializable if the provided<a name="line.206"></a>
<span class="sourceLineNo">207</span>   * {@code Funnel&lt;T&gt;} is.<a name="line.207"></a>
<span class="sourceLineNo">208</span>   *<a name="line.208"></a>
<span class="sourceLineNo">209</span>   * &lt;p&gt;It is recommended the funnel is implemented as a Java enum. This has the benefit of ensuring<a name="line.209"></a>
<span class="sourceLineNo">210</span>   * proper serialization and deserialization, which is important since {@link #equals} also relies<a name="line.210"></a>
<span class="sourceLineNo">211</span>   * on object identity of funnels.<a name="line.211"></a>
<span class="sourceLineNo">212</span>   *<a name="line.212"></a>
<span class="sourceLineNo">213</span>   * @param funnel the funnel of T's that the constructed {@code BloomFilter&lt;T&gt;} will use<a name="line.213"></a>
<span class="sourceLineNo">214</span>   * @param expectedInsertions the number of expected insertions to the constructed<a name="line.214"></a>
<span class="sourceLineNo">215</span>   *     {@code BloomFilter&lt;T&gt;}; must be positive<a name="line.215"></a>
<span class="sourceLineNo">216</span>   * @param fpp the desired false positive probability (must be positive and less than 1.0)<a name="line.216"></a>
<span class="sourceLineNo">217</span>   * @return a {@code BloomFilter}<a name="line.217"></a>
<span class="sourceLineNo">218</span>   */<a name="line.218"></a>
<span class="sourceLineNo">219</span>  public static &lt;T&gt; BloomFilter&lt;T&gt; create(<a name="line.219"></a>
<span class="sourceLineNo">220</span>      Funnel&lt;T&gt; funnel, int expectedInsertions /* n */, double fpp) {<a name="line.220"></a>
<span class="sourceLineNo">221</span>    checkNotNull(funnel);<a name="line.221"></a>
<span class="sourceLineNo">222</span>    checkArgument(expectedInsertions &gt;= 0, "Expected insertions (%s) must be &gt;= 0",<a name="line.222"></a>
<span class="sourceLineNo">223</span>        expectedInsertions);<a name="line.223"></a>
<span class="sourceLineNo">224</span>    checkArgument(fpp &gt; 0.0, "False positive probability (%s) must be &gt; 0.0", fpp);<a name="line.224"></a>
<span class="sourceLineNo">225</span>    checkArgument(fpp &lt; 1.0, "False positive probability (%s) must be &lt; 1.0", fpp);<a name="line.225"></a>
<span class="sourceLineNo">226</span>    if (expectedInsertions == 0) {<a name="line.226"></a>
<span class="sourceLineNo">227</span>      expectedInsertions = 1;<a name="line.227"></a>
<span class="sourceLineNo">228</span>    }<a name="line.228"></a>
<span class="sourceLineNo">229</span>    /*<a name="line.229"></a>
<span class="sourceLineNo">230</span>     * TODO(user): Put a warning in the javadoc about tiny fpp values,<a name="line.230"></a>
<span class="sourceLineNo">231</span>     * since the resulting size is proportional to -log(p), but there is not<a name="line.231"></a>
<span class="sourceLineNo">232</span>     * much of a point after all, e.g. optimalM(1000, 0.0000000000000001) = 76680<a name="line.232"></a>
<span class="sourceLineNo">233</span>     * which is less that 10kb. Who cares!<a name="line.233"></a>
<span class="sourceLineNo">234</span>     */<a name="line.234"></a>
<span class="sourceLineNo">235</span>    long numBits = optimalNumOfBits(expectedInsertions, fpp);<a name="line.235"></a>
<span class="sourceLineNo">236</span>    int numHashFunctions = optimalNumOfHashFunctions(expectedInsertions, numBits);<a name="line.236"></a>
<span class="sourceLineNo">237</span>    try {<a name="line.237"></a>
<span class="sourceLineNo">238</span>      return new BloomFilter&lt;T&gt;(new BitArray(numBits), numHashFunctions, funnel,<a name="line.238"></a>
<span class="sourceLineNo">239</span>          BloomFilterStrategies.MURMUR128_MITZ_32);<a name="line.239"></a>
<span class="sourceLineNo">240</span>    } catch (IllegalArgumentException e) {<a name="line.240"></a>
<span class="sourceLineNo">241</span>      throw new IllegalArgumentException("Could not create BloomFilter of " + numBits + " bits", e);<a name="line.241"></a>
<span class="sourceLineNo">242</span>    }<a name="line.242"></a>
<span class="sourceLineNo">243</span>  }<a name="line.243"></a>
<span class="sourceLineNo">244</span><a name="line.244"></a>
<span class="sourceLineNo">245</span>  /**<a name="line.245"></a>
<span class="sourceLineNo">246</span>   * Creates a {@code Builder} of a {@link BloomFilter BloomFilter&lt;T&gt;}, with the expected number<a name="line.246"></a>
<span class="sourceLineNo">247</span>   * of insertions, and a default expected false positive probability of 3%.<a name="line.247"></a>
<span class="sourceLineNo">248</span>   *<a name="line.248"></a>
<span class="sourceLineNo">249</span>   * &lt;p&gt;Note that overflowing a {@code BloomFilter} with significantly more elements<a name="line.249"></a>
<span class="sourceLineNo">250</span>   * than specified, will result in its saturation, and a sharp deterioration of its<a name="line.250"></a>
<span class="sourceLineNo">251</span>   * false positive probability.<a name="line.251"></a>
<span class="sourceLineNo">252</span>   *<a name="line.252"></a>
<span class="sourceLineNo">253</span>   * &lt;p&gt;The constructed {@code BloomFilter&lt;T&gt;} will be serializable if the provided<a name="line.253"></a>
<span class="sourceLineNo">254</span>   * {@code Funnel&lt;T&gt;} is.<a name="line.254"></a>
<span class="sourceLineNo">255</span>   *<a name="line.255"></a>
<span class="sourceLineNo">256</span>   * @param funnel the funnel of T's that the constructed {@code BloomFilter&lt;T&gt;} will use<a name="line.256"></a>
<span class="sourceLineNo">257</span>   * @param expectedInsertions the number of expected insertions to the constructed<a name="line.257"></a>
<span class="sourceLineNo">258</span>   *     {@code BloomFilter&lt;T&gt;}; must be positive<a name="line.258"></a>
<span class="sourceLineNo">259</span>   * @return a {@code BloomFilter}<a name="line.259"></a>
<span class="sourceLineNo">260</span>   */<a name="line.260"></a>
<span class="sourceLineNo">261</span>  public static &lt;T&gt; BloomFilter&lt;T&gt; create(Funnel&lt;T&gt; funnel, int expectedInsertions /* n */) {<a name="line.261"></a>
<span class="sourceLineNo">262</span>    return create(funnel, expectedInsertions, 0.03); // FYI, for 3%, we always get 5 hash functions<a name="line.262"></a>
<span class="sourceLineNo">263</span>  }<a name="line.263"></a>
<span class="sourceLineNo">264</span><a name="line.264"></a>
<span class="sourceLineNo">265</span>  /*<a name="line.265"></a>
<span class="sourceLineNo">266</span>   * Cheat sheet:<a name="line.266"></a>
<span class="sourceLineNo">267</span>   *<a name="line.267"></a>
<span class="sourceLineNo">268</span>   * m: total bits<a name="line.268"></a>
<span class="sourceLineNo">269</span>   * n: expected insertions<a name="line.269"></a>
<span class="sourceLineNo">270</span>   * b: m/n, bits per insertion<a name="line.270"></a>
<span class="sourceLineNo">271</span><a name="line.271"></a>
<span class="sourceLineNo">272</span>   * p: expected false positive probability<a name="line.272"></a>
<span class="sourceLineNo">273</span>   *<a name="line.273"></a>
<span class="sourceLineNo">274</span>   * 1) Optimal k = b * ln2<a name="line.274"></a>
<span class="sourceLineNo">275</span>   * 2) p = (1 - e ^ (-kn/m))^k<a name="line.275"></a>
<span class="sourceLineNo">276</span>   * 3) For optimal k: p = 2 ^ (-k) ~= 0.6185^b<a name="line.276"></a>
<span class="sourceLineNo">277</span>   * 4) For optimal k: m = -nlnp / ((ln2) ^ 2)<a name="line.277"></a>
<span class="sourceLineNo">278</span>   */<a name="line.278"></a>
<span class="sourceLineNo">279</span><a name="line.279"></a>
<span class="sourceLineNo">280</span>  /**<a name="line.280"></a>
<span class="sourceLineNo">281</span>   * Computes the optimal k (number of hashes per element inserted in Bloom filter), given the<a name="line.281"></a>
<span class="sourceLineNo">282</span>   * expected insertions and total number of bits in the Bloom filter.<a name="line.282"></a>
<span class="sourceLineNo">283</span>   *<a name="line.283"></a>
<span class="sourceLineNo">284</span>   * See http://en.wikipedia.org/wiki/File:Bloom_filter_fp_probability.svg for the formula.<a name="line.284"></a>
<span class="sourceLineNo">285</span>   *<a name="line.285"></a>
<span class="sourceLineNo">286</span>   * @param n expected insertions (must be positive)<a name="line.286"></a>
<span class="sourceLineNo">287</span>   * @param m total number of bits in Bloom filter (must be positive)<a name="line.287"></a>
<span class="sourceLineNo">288</span>   */<a name="line.288"></a>
<span class="sourceLineNo">289</span>  @VisibleForTesting<a name="line.289"></a>
<span class="sourceLineNo">290</span>  static int optimalNumOfHashFunctions(long n, long m) {<a name="line.290"></a>
<span class="sourceLineNo">291</span>    return Math.max(1, (int) Math.round(m / n * Math.log(2)));<a name="line.291"></a>
<span class="sourceLineNo">292</span>  }<a name="line.292"></a>
<span class="sourceLineNo">293</span><a name="line.293"></a>
<span class="sourceLineNo">294</span>  /**<a name="line.294"></a>
<span class="sourceLineNo">295</span>   * Computes m (total bits of Bloom filter) which is expected to achieve, for the specified<a name="line.295"></a>
<span class="sourceLineNo">296</span>   * expected insertions, the required false positive probability.<a name="line.296"></a>
<span class="sourceLineNo">297</span>   *<a name="line.297"></a>
<span class="sourceLineNo">298</span>   * See http://en.wikipedia.org/wiki/Bloom_filter#Probability_of_false_positives for the formula.<a name="line.298"></a>
<span class="sourceLineNo">299</span>   *<a name="line.299"></a>
<span class="sourceLineNo">300</span>   * @param n expected insertions (must be positive)<a name="line.300"></a>
<span class="sourceLineNo">301</span>   * @param p false positive rate (must be 0 &lt; p &lt; 1)<a name="line.301"></a>
<span class="sourceLineNo">302</span>   */<a name="line.302"></a>
<span class="sourceLineNo">303</span>  @VisibleForTesting<a name="line.303"></a>
<span class="sourceLineNo">304</span>  static long optimalNumOfBits(long n, double p) {<a name="line.304"></a>
<span class="sourceLineNo">305</span>    if (p == 0) {<a name="line.305"></a>
<span class="sourceLineNo">306</span>      p = Double.MIN_VALUE;<a name="line.306"></a>
<span class="sourceLineNo">307</span>    }<a name="line.307"></a>
<span class="sourceLineNo">308</span>    return (long) (-n * Math.log(p) / (Math.log(2) * Math.log(2)));<a name="line.308"></a>
<span class="sourceLineNo">309</span>  }<a name="line.309"></a>
<span class="sourceLineNo">310</span><a name="line.310"></a>
<span class="sourceLineNo">311</span>  private Object writeReplace() {<a name="line.311"></a>
<span class="sourceLineNo">312</span>    return new SerialForm&lt;T&gt;(this);<a name="line.312"></a>
<span class="sourceLineNo">313</span>  }<a name="line.313"></a>
<span class="sourceLineNo">314</span><a name="line.314"></a>
<span class="sourceLineNo">315</span>  private static class SerialForm&lt;T&gt; implements Serializable {<a name="line.315"></a>
<span class="sourceLineNo">316</span>    final long[] data;<a name="line.316"></a>
<span class="sourceLineNo">317</span>    final int numHashFunctions;<a name="line.317"></a>
<span class="sourceLineNo">318</span>    final Funnel&lt;T&gt; funnel;<a name="line.318"></a>
<span class="sourceLineNo">319</span>    final Strategy strategy;<a name="line.319"></a>
<span class="sourceLineNo">320</span><a name="line.320"></a>
<span class="sourceLineNo">321</span>    SerialForm(BloomFilter&lt;T&gt; bf) {<a name="line.321"></a>
<span class="sourceLineNo">322</span>      this.data = bf.bits.data;<a name="line.322"></a>
<span class="sourceLineNo">323</span>      this.numHashFunctions = bf.numHashFunctions;<a name="line.323"></a>
<span class="sourceLineNo">324</span>      this.funnel = bf.funnel;<a name="line.324"></a>
<span class="sourceLineNo">325</span>      this.strategy = bf.strategy;<a name="line.325"></a>
<span class="sourceLineNo">326</span>    }<a name="line.326"></a>
<span class="sourceLineNo">327</span>    Object readResolve() {<a name="line.327"></a>
<span class="sourceLineNo">328</span>      return new BloomFilter&lt;T&gt;(new BitArray(data), numHashFunctions, funnel, strategy);<a name="line.328"></a>
<span class="sourceLineNo">329</span>    }<a name="line.329"></a>
<span class="sourceLineNo">330</span>    private static final long serialVersionUID = 1;<a name="line.330"></a>
<span class="sourceLineNo">331</span>  }<a name="line.331"></a>
<span class="sourceLineNo">332</span>}<a name="line.332"></a>




























































</pre>
</div>
</body>
</html>
